Christine Erbe – Curtin University,
Miles Parsons – Curtin University and Australian Institute of Marine Science,
Alec Duncan – Curtin University,
Klaus Lucke – Curtin University and JASCO Applied Sciences,
Alexander Gavrilov – Curtin University,
Kim Allen – THHINK Autonomous Systems,

Centre for Marine Science & Technology, Curtin University, Bentley, 6102 Western Australia, AUSTRALIA|

Popular version of paper 1aAO5
Presented Monday morning, May 7, 2018, 11:10-11:25 a.m., GREENWAY A
175th ASA Meeting, Minneapolis, MN

Underwater sound contains a lot of information about the source that produces it. Ships, for example, have a characteristic sound signature underwater, by which the type of vessel, its speed, and its route can easily be determined. In some cases, individual vessels can be identified by their sound and information about the type of propulsion, operational mode, and load can be deduced and maintenance issues (e.g., relating to the propeller) can be picked out. Similarly, just by listening, we can study marine life from whales to fishes and shrimp; we can track their movements; monitor their behavior; and in the case of some species of dolphins, even say which family and individuals are there. Sound is an important commodity for marine life; marine mammals as well as fishes, for example, communicate through sound, sense their environment, navigate, and forage—all mediated by sound.

Video 1: Underwater video and sound recording of different water sports activities.

Given the important role sound plays in the life functions of marine fauna, the potential interference by man-made noise has received growing interest. Noise may disrupt animal behavior, affect their hearing abilities, mask communication, cause stress, and in extreme cases cause physical and physiological damage that can ultimately be fatal. The research and management focus has—quite sensibly—been on the strongest sources, such as geophysical surveys or coastal and marine construction. Non-motorised activities are expected quieter and have hardly been studied.

Within the framework of an underwater acoustic project, we had the opportunity to record ourselves and friends performing a number of recreational water sports activities in a quiet Olympic pool, with all surrounding machinery (including cleaning pumps) switched off [1,2]. Specifically, different people were filmed and acoustically recorded while swimming breaststroke, backstroke, freestyle, and butterfly; snorkeling with and without fins; paddling a surfboard with alternating single or double arms; scuba diving; kayaking; and jumping into the pool. Sound pressure and water particle velocity were measured.

Activities that occurred at the surface, involved repeatedly piercing the surface and hence created bubble clouds were the strongest sound generators. Received levels were 110-131 dB re 1 µPa (10-16,000 Hz) for all of the activities at the closest point of approach (1 m). Levels were lower than those found in environmental noise regulations, but were clearly above ambient noise levels recorded off beaches and hence predicted audible by marine fauna over tens to hundreds of meters.

The characterization and quantification of underwater sound from recreational water sports has applicability well beyond environmental management. For example, just by listening to the recordings, it is easy to identify who of the volunteers was in the pool and which activity (including which style of swimming, with or without fins, with single versus double arms, etc.) was performed. The better (i.e., faster and smoother) swimmers were the quieter swimmers. Underwater sound might be a useful tool to assess professional or competitive swimmer performance and can be used for security monitoring of pools.

[1] C. Erbe, M. Parsons, A. J. Duncan, K. Lucke, A. Gavrilov and K. Allen, “Underwater particle motion (acceleration, velocity and displacement) from recreational swimmers, divers, surfers and kayakers,” Acoustics Australia 45,  293-299 (2017). doi: 10.1007/s40857-017-0107-6

[2] C. Erbe, M. Parsons, A. J. Duncan and K. Allen, “Underwater acoustic signatures of recreational swimmers, divers, surfers and kayakers,” Acoustics Australia 44 (2),  333-341 (2016). doi: 10.1007/s40857-016-0062-7

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